The acoustic performance of glazing assemblies is expressed in two terms:

Sound Transmission Class (STC) is used to measure the sound transmission loss of interior walls, ceilings and floors.

Outdoor-Indoor Transmission Class (OITC) measures the sound transmission loss of exterior glazing applications.

High sound transmission loss—good sound insulation—is desired in many commercial curtain wall applications. Limiting sound transmission through glazing requires review and testing of the entire glazing system.

Laminated glass and insulating glass tend to produce higher OITC ratings because the laminate dampens vibration and the air space limits sound transmission.